Conductive supports for electrophotographic light-sensitive materials generally used include papers; aluminum plates; polymer films or papers which have metals vapor-deposited thereon such as aluminum or palladium; polymer films or papers having vapor-deposited thereon a semiconductor such as tin-doped indium oxide, or antimony-doped tin oxide; and polymer films containing cuprous iodide. An interlayer is often formed between such a support and the photoconductive layer formed thereon. The interlayer can have electric hindrance characteristics and is used to prevent the occurence of harmful electric co-action between a photoconductive layer and a conductive layer and for improving various electrophotographic characteristics such as dark decay, fatigue, light sensitivity, charging property, etc. Intermediate layers suitable for the purpose are discharged in various technical reports, e.g., U.S. Pat. Nos. 2,901,348; 3,573,906; 3,640,708; etc.
However, conventional materials for the interlayers may be effective with respect to reducing the occurence of dark decay and improving the charging property but is not always satisfactory with respect to increasing electrophotographic sensitivity. Also, in many cases, conventional materials for interlayers are soluble in a coating solvent for a photoconductive layer, such as toluene, xylene, methylene chloride, chloroform, tetrachloroethane, dichloroethane, chlorobenzene, tetrahydrofuran (THF), dioxane, cyclohexanone, etc., and further when a conductive layer disposed under the interlayer is a conductive layer of a binder dispersed type, e.g., a layer composed of cuprous iodide dispersed in a binder, the binder is soluble in a coating solvent for a photoconductive layer, which results in causing various troubles. More specifically, difficulties result from coating the photoconductive layer in that the interlayer may be destroyed by the coating solvent for the photoconductive layer and further the conductive layer coated under the layer may also be destroyed which reduces the electrophotographic sensitivity. Also, since the interlayer is locally intermixed with the photo-conductive layer, it is difficult to uniformly coat the photo-conductive layer, thereby an ununiform and uneven photoconductive layer is formed. Thus, undesirable uneven charging occurring during an electrophotographic process, uneven density occurring during development, etc., may take place.
It is difficult to obtain a bipolar electrophotographic light-sensitive material having practically satisfactory properties using conventional materials for the interlayer. By the term "bipolar electrophotographic light-sensitive material" is meant an electrophotographic material which maintains a desired surface charged potential and has practical electrophotographic sensitivity under either positive or negative polar charges. When using bipolar electrophotographic light-sensitive material, either normal development or a reversal development can be easily performed in the same electrophotographic process merely by changing the positive charge polarity and negative charge polarity using a developing toner having the same polarity. Accordingly, the electrophotographic light-sensitive material has a wide application range in electrophotography.
A gelatin layer is insoluble in a coating solvent for a photoconductive layer and hence it protects a conductive layer. Furthermore, the gelatin layer acts to prevent the intermixing of a positive carrier into a photoconductive layer from a conductive layer and also makes possible negative charging.
Also, since there is no local mixing between the photoconductive layer and gelatin layer, uneven coating does not occur.